Here's how massive Star Wars Episode I: The Phantom Menace is. This week, the main film running against it is a new print of Carol Reed's The Third Man. And, for its opening night in London, the word is that a zither player will perform live, twanging away as the audience files in. But the poor guy's instructions are that he has to play... John Williams's theme from Star Wars.

Ah, the John Williams theme from Star Wars! What a substantial muzak-ed aggregate of our adult lives has been played out in lifts and supermarkets to that inspired air with its exclamatory dotted rhythm - a melody as bold and genially vainglorious as anything by Aaron Copland. How American it is, how unashamedly forthright, and how far it has infiltrated our cultural lives since being a showstopper for the Boston Pops in the late 70s. By God, even now, my heart leaps like a salmon to hear it - just as it did when I first got a load of it in the summer of 1977, in a shopping mall movie theatre in Cambridge, Massachusetts, and it is with some austere restraint I deny myself here the full portion of 30-something reverie.

Suffice it to say that I remember Star Wars just before it became massive in the UK, when some of us clueless types over here thought you pronounced it with the accent on the second word in the British style, like Hong Kong! Hell, no limey: it's Hong Kong, cigarette, and Star Wars. Except now it's pronounced "Four".

Phantom Menace is the biggest and most prestigious prequel in commercial cinema history. Short of discovering a Shakespeare play called Young Prince Lear, the excitement or, at any rate, the hype, could hardly be matched.

As all the world knows, this is to form a gigantic sequence of six movies, spanning Phantom Menace to Return Of The Jedi. Whether or not audiences will be encouraged to actually watch them in sequence is a moot point as, exactly halfway through, the technology and style will suddenly regress to the naff age of President Jimmy Carter. It will be like playing Tomb Raider and finding that the fourth level is PacMan. Be that as it may, we kick off at the dawn of recorded time with two cowled, monkish figures, their spartan appearance bespeaking a certain manly and moral severity. They are Qui-Gon Jinn (Liam Neeson) and young, fresh-faced, not-old-yet Obi-Wan Kenobi (Ewan McGregor), who are, respectively, officer and novitiate of that notoriously unelected oligarchy, the Jedi Knights.

Members of this quasi-Masonic sect presume to style themselves the guardians of peace and justice in the galaxy on the basis of startling, but not limitless, parapsychological powers and martial dexterity with lightsabres; waving about this preposterously inefficient weaponry being sufficient to subdue large numbers of hostile automaton warriors or "droids".

Here, of course, I am guilty of the vulgar, pedantic heresy of taking the naturalistic conventions of Star Wars at face value and disingenuously teasing out their contradictions for facetious effect. Star Wars fans will know that this comic seam has already been exhaustively mined by Kevin Smith in his movies Clerks and Mallrats - and a little bit by Justin Kerrigan's Human Traffic - riffing playfully on bits of the series in a stoned or baffled way. It is too easily done with any scene, taken almost at random, and I shall now desist.

Qui-Gon and Obi-Wan have arrived to broker a peace process between the inoffensive little planet of Naboo, and the ruthlessly commercial Trade Federation, which is blockading it and preparing to wage war on Naboo for its mercantile ends. The two Jedis' diplomacy is sabotaged; the invasion begins and Qui-Gon Jinn and Kenobi smuggle themselves down on to the planet, where they befriend a clumsy but lovable native creature called Jar Jar Binks, who helps them rescue the beautiful Queen of Naboo (Natalie Portman). They spirit her away to the remote planet of Tatooine - that harsh desert landscape where no one needs sunglasses - where they chance to befriend a young slave boy, Anakin Skywalker, for whom the force is very strong.

Young Ani deeply impresses Qui-Gon with his obvious eligibility to be inducted into the Jedis - and yet, ooo-er, there is a bit of a bad vibe about this, which the entire audience is picking up on. But not Qui-Gon and pert young Ben Kenobi. More of this presently.

We have to start somewhere, and I will start with the acting. It is simply, uniformly, astonishingly bad. Liam Neeson is on Mogadon. He doesn't just phone in his performance, he puts it in the post without enough stamps on it; he Sellotapes it to the leg of a pigeon. Ewan McGregor does the same: a boring, misguided solemnity, and a plum-in-the-mouth English accent I can only assume is a sort of backdated Alec Guinness. He would have done better to copy the young Guinness from, say, The Man in the White Suit - at least we might have had something with freshness and fun. It is not their fault, however. Director George Lucas has clearly made a decision to exclude any spice or vinegar in the bland, universally acceptable Diet Coke he wishes to sell all over the world.

The number of Brits in the cast is a residual surprise. There are plenty of familiar faces, including Naboo starfighter pilots played by Ralph Brown (Danny from Withnail and I) and - incredibly - Celia Imrie. Yes, that's right: Miss Babs at the controls of a starfighter. Weird.

In Phantom Menace, the concepts of "acting" and "FX" have effectively become conflated, as a number of the supporting cast are non-human. This used to mean some tiny or limbless unfortunate sweating in a hairy costume in Shepperton or Borehamwood - and then, in the traditional Lucas/Spielberg manner, being chillingly excluded from the film's promotional material lest their real presence damage the picturesque illusion.

Now a real actor need only be the template for the digitally animated version. This is most prominently the case with Jar Jar Binks, a great lunk of a creature, with great eyes out on stalks, and a sloppy, goofy good nature. He is fantastically irritating, with an all-but-unintelligible accent with which he says things like: "We's a goin' home!" and "Me's a scaaaared!"

I need hardly say Jar Jar is supposed to be black: or rather he is a kind of interplanetary, convenient Lucasfilms-variant on black. With his comic subordinate status, he is the foil to the pretty Wasp heroes: the Queen and the Jedis. Jar Jar is an old-fashioned token black, a real eye-rolling yessuh-massa character to boot, with everything but the actual pigment. But wait. Watto, the hook-nosed Toydarian on Tatooine is clearly quasi-Jewish in the same way: a slave-owner. Is the ordinary commercial racism submerged in Phantom Menace compounded with a creepy, unacknowledged pseudo-political correctness?

The effects themselves are naturally impressive, and there is a lot of fun in the Pod Race scene: a cheerful steal from Ben-Hur. But, however dazzling they are, the effects are essentially a development of the Industrial Light and Magic techniques that first blew us away in Jurassic Park in 1993, which, in movie terms, is a long time ago, in a galaxy far, far away. There has been no quantum leap since then. And, in any case, it is difficult to praise effects which have made acting and script so utterly subordinate.

The strangest character is Anakin Skywalker himself. We all know that he is going to grow up to be the sinister, tragic Darth Vader. Some publicity stills actually show his mop of hair casting a shadow like Darth's famous helmet. Yet this image does not appear in the film and the strange ominous pall that hangs over young Ani would be baffling to anyone who does not realise that we must rely, as it were, on extra-textual clues. We have to know the hype, to have read the hype: the hype is an essential part of the package.

And this is why Phantom Menace is, ultimately, so extraordinarily objectionable. It treats us like fans, not an audience. It takes our slavish consumer status for granted and does not feel the need to do any real work to engage us, to make us care about the story or the characters. It's all FX and merchandise.

Nothing has the right to bore and disappoint us this much. And when it's finally over - and I found myself looking at my watch, with my eyelids very heavy - we get an ending which is neither satisfactory closure, nor cliffhanger, just the end of one episode in a massive, self-satisfied TV series; a TV series which deserves to be cancelled.